This invention relates to a communication system in which communication is established via communication cables and in which a predetermined connection procedure is executed when a communication cable is connected with a communication device. In particular, this invention relates to a communication system in which a communication cable is connected/disconnected with a communication device while the communication device is active.
In a communication system in which communication is established via a cable, a predetermined connection procedure generally has to be executed when the cable is connected with a device. In particular, if two devices whose transmission rates are different from each other are to establish communication between them, the connection procedure has to include a step for arbitrating transmission rates (transmission rate arbitration).
It is assumed that first and second upper devices (e.g. LSIs) are connected with each other via a communication cable in above-mentioned communication system. Each of the first and second upper devices needs a set of Large Scale Integrator (LSI) for physical layer and a transceiver as serial interface. Namely, the first upper device is connected with first physical layer LSI via first transceiver and the second upper device is connected with second physical layer LSI via second transceiver. The first and second transceivers are connected with each other via the communication cable. The first and second physical layer LSIs operate as serial interfaces.
If transmission rate of first physical layer LSI (first transmission rate) and that of second physical layer LSI (second transmission rate) are different from each other, transmission rate arbitration is required for the first and second physical layer LSIs. For example, if the maximum of the first transmission rate is 400 Mbps and the maximum of the second transmission rate is 200 Mbps, the transmission rate arbitration is executed between the first and second physical layer LSIs to harmonize transmission rate between them at 200 Mbps when they are connected with each other via the communication cable.
In this communication system, the connection procedure including the transmission rate arbitration is immediately required every time the communication cable is connected. However, connection/disconnection between a communication cable and device often causes noise that makes it hard to guarantee end of the connection procedure including the transmission rate arbitration. Especially, when the system is an optical communication system, noise caused on cable connection/disconnection adversely affects light, and consequently, it becomes harder to guarantee the end of the connection procedure.